The invention relates to blends of olefin polymers and syndiotactic polyvinyl aromatic polymers and/or syndiotactic polymethacrylate esters, which have a finely dispersed distribution of the blend components, a high dimensional stability at elevated temperatures and an improved printability and paintability, as well as to a method for their production.
Blends of olefin polymers and conventional atactic polyvinyl aromatic polymers and/or conventional isotactic polymethacrylate esters are known. The thermodynamic incompatibility of the components of the blend is responsible for the coarsely dispersed structure and the unsatisfactory material properties of the blends (Benderly, D., J. Mater. Sci. Lett. 1996, 15 (15), 1349-1352). To achieve a finely dispersed structure of the blend components, compatibilizers are added, which bring about a partial compatibility of the components at the phase boundary.
For blends of polyethylene and atactic polystyrene, a compatibilization of the incompatible components is achieved by the admixing of styrene-ethylene/propylene diblock copolymers (Domininghaus, H., Gummi-Fasem-Kunststoffe 45 (1992) 7, 352-357) or of styrene-ethylene/butadiene-styrene triblock copolymers (Yang, L., J. Appl. Polymer Sci. 58 (1995), 117-127).
Likewise, the reactive extrusion of polyethylene with polystyrene in the presence of peroxides and cross linking co-agents (EP 0 210 306; Rudin, A., Polymer Engng. Sci. 32 (1992) 1678-1686) as well of styrene-vinylbenzaldehyde copolymers as co-components (Rudin, A., Polymer Engng. Sci. 28 (1988) 21, 1434-1442) leads to an improvement in the compatibility of the components, since the compatibilizer is formed in situ by the partial cross linking of the components.
Blends of ethylenecycloolefin copolymers, such as ethylene-norbornene copolymers with atactic polystyrene are also known (DD 223 721).
Inhomogeneous blends are furthermore formed by the thermoplastic processing of mixtures of isotactic polypropylene and atactic polystyrene (Fortelny, I., J. Applied Polymer Sci. 59 (1996) 155-164).
Known methods of compatibilizing blends of isotactic polypropylene and atactic polystyrene are the addition of styrene-grafted polypropylene (EP 0 435 340), styrene-grafted elastomeric polypropylene (EP 0 640 650), elastomeric polybutene (PCT-WO 94 28 066), hydrogenated isoprene-styrene block copolymers (JP 06 049 261), styrene-ethylene/butadiene-styrene block copolymers (JP 04 045 140) and of styrene/butadiene block copolymers (JP 06 271 717; Navratilova, E., Polym. Networks Blends 6 (1996) 3, 127-133).
Furthermore, effective, known compatibilizers in blends of isotactic polypropylene and atactic polystyrene are segmented copolymers, which are formed by the reaction of styrene-maleic anhydride copolymers with amino-functionalized polypropylene (PCT-WO 93 02 140) or anhydride-functionalized polypropylene (JP 04 053 853), by the reaction of hydrogenated butadiene-styrene block copolymers, modified with maleic anhydride, with polypropylene functionalized with epoxy groups (JP 04 266 953), by reaction of polystyrene, modified with glycidyl groups, and polypropylene, modified with acid anhydride groups (JP 05 179 094) or by reaction of styrene-maleic anhydride copolymers with polypropylene, modified with acid anhydride, and bifunctional compounds of opposite reactivity (JP 05 209 096).
A reactive compatibilization of isotactic polypropylene with atactic polystyrene is accomplished by reaction with peroxides in the melt (JP 59 226 042), optionally in the presence of styrene-grafted polypropylene (JP 04 041 614) or in the presence of aromatic vinyl monomers (JP 05 140 245).
An increased compatibility of polypropylene-polystyrene blends is also achieved by forming the atactic polystyrene components in situ by the free radical styrene polymerization in the presence of dispersed polypropylene (EP 0 435 340).
It is also known that compatible blends may be produced from polypropylene and polystyrene in situ by a special polymerization technology using Ziegler-Natta catalysts ("reactor blend"); however, the polystyrene component formed is also an atactic polymer (Modem Plastics Intern. (1996) 3, 27; (1996) 4, 93).
For blends of polypropylene and polymethylmethacrylate, the addition of reaction products of amino-functionalized polypropylene and styrene-maleic anhydride copolymers as compatibilizers, for achieving partial compatibility of the components, is described (WO 93 02140).
For blends of poly-4-methylpentene, poly-1-butene or polypropylene with poly(methyl methacrylate), the corresponding azlactone-grafted polyolefins represent suitable compatibilizers for the thermodynamically incompatible blend components (U.S. Pat. No. 5,262,484).
It is furthermore known that polypropylene-poly(methyl methacrylate) block copolymers may be used to improve the material properties of polypropylene-poly(methyl methacrylate) blends (Hosoda, S., Polymer J. 1991 (23), 277). These block copolymers can be synthesized by the complex coordinative polymerization of propylene in the presence of ethylene-bis-(tetrahydroindenyl) zirconium dichloride/aluminoxane catalysts, reaction of the terminal ethylene groups with magnesium bromide and use of the modified polypropylene as macromolecular initiator for the anionic polymerization of methyl methacrylate (Shiono. T., Macromolecules 1994 (27) 6229-6231).
Blends of olefin polymers and conventional, atactic polyvinyl aromatic polymers and conventional isotactic polymethacrylate esters furthermore have the disadvantage that the dimensional stability of these blends at elevated temperatures is limited by the low softening temperatures of the atactic polyvinyl aromatic polymers or the isotactic polymethacrylate esters. For example, the softening temperature of the conventional, atactic polyvinyl aromatic polymers, polystyrene, is 90.degree.-100.degree. C., of poly-4-chlorostyrene 120.degree.-128.degree. C., of poly-4-methoxystyrene 80.degree.-90.degree. C. and of poly-.alpha.-methylstyrene 180.degree.-185.degree. C. and the softening temperature of the conventional isotactic polymethacrylate esters, polymethacrylate is 160.degree. C. and of poly-(t-butyl methacrylate) 104.degree. C. (Brandrup-Immergut, Polymer Handbook, Interscience Publishers New York, 1989).
A further decrease in dimensional stability at elevated temperatures is brought about by the furthermore used elastomeric compatibilizer components in the blends of olefin polymers and conventional vinyl polymers.
Compared to the usual atactic polyvinyl aromatic polymers or the usual isotactic polymethacrylate esters, highly ordered syndiotactic polyvinyl aromatic polymers or polymethacrylate esters have a significantly higher crystallite melting temperature. For example, the melting temperature of isotactic polystyrene is of the order of 210.degree. to 225.degree. C., of syndiotactic polystyrene 255.degree. to 270.degree. C., of syndiotactic poly(methyl methacrylate) approximately 200.degree. C. and of syndiotactic poly-(t-butyl methacrylate) approximately 165.degree. C.
Methods of synthesizing syndiotactic polyvinyl aromatic polymers and syndiotactic polymethacrylate esters are known.
Known methods of synthesizing syndiotactic polystyrene are the free radical polymerization of styrene at temperatures below -65.degree. C. (Doi, Y., Macromolecules 19 (1986), 289), as well as the complex coordinative polymerization in the presence of aluminum alkyl/titanium halides at temperatures below -65.degree. C. (Natta, G., J. Amer. Chem. Soc. 84 (1962), 1488).
Catalyst systems of aluminum alkyl/cyclopentadienyl titanium alcoholates with alkyl aluminoxanes as co-catalysts bring about the complex coordinative polymerization of styrene already at room temperature and also at elevated temperatures, formation of syndiotactic polystyrene (EP 0 210 616). The molecular weight distribution of the syndiotactic polystyrene can be broadened by the use of mixtures of cyclopentadienyl titanates (EP 0 420 134). High yields are achieved if a catalyst system of hydro-tris-pyrazolyl borate and cyclopentadienyl titanium dimethoxide is used as titanium component at an Al/Ti ratio of 400 (EP 0 617 052).
Suitable catalyst systems for the polymerization of methacrylate esters with formation of syndiotactic products are vanadyl trichloride/methyl aluminoxanes and vanadic acetyl acetonate/methyl aluminoxane (Endo, K., Macromol. Rapid Commun. 15, 893-896; Macromol. Chem. Phys. 196 (1995), 2065-2072) and dicyclopentadienyl zirconium dichloride/methyl aluminoxane (Deng, H., Macromol. Chem. Phys. 196 (1995), 1971-1980).
Problems with the melt homogenization of polyolefins with syndiotactic polyvinyl aromatic polymers or syndiotactic polymethacrylate esters arise out of the highly diverging melting points of the polyolefins (polyethylene 112.degree.-125.degree. C., isotactic polybutene 124.degree.-130.degree. C., isotactic polypropylene 159.degree.-161.degree. C.) and of the syndiotactic aromatic vinyl polymers (&gt;250.degree. C.) or the syndiotactic polymethacrylate esters (&gt;165.degree. C.).
The preparation of blends of olefin polymers and syndiotactic vinyl polymers and/or syndiotactic polymethacrylate esters in situ using known catalysts systems for the catalytic polymerization of the corresponding monomers and known reaction conditions does not lead to any result.
It is an object of the present invention to develop blends of olefin polymers and syndiotactic polyvinyl aromatic polymers and/or syndiotactic polymethacrylate esters, which have a finely dispersed distribution of the components of the blend, a high dimensional stability at elevated temperatures and an improved printability and paintability, as well as a method for preparing them.